1.2 Predefined Classes

SOS provides a rich set of predefined classes that can be used to specialize methods to any of Scheme’s built-in datatypes.

Class: <object>

This is the class of all Scheme objects. It has no direct superclasses, and all other classes are subclasses of this class.

Class: <instance>

This is the class of instances. It is a direct subclass of <object>. The members of this class are the objects that satisfy the predicate instance?.

Class: <boolean>

Class: <char>

Class: <entity>

Class: <pair>

Class: <procedure>

Class: <record>

Class: <string>

Class: <symbol>

Class: <vector>

These are the classes of their respective Scheme objects. They are all direct subclasses of <object>. The members of each class are the objects that satisfy the corresponding predicate; for example, the members of <procedure> are the objects that satisfy procedure?.

Class: <generic-procedure>

This is the class of generic procedure instances. It is a direct subclass of <procedure>.

Class: <method>

This is the class of method objects. It is a direct subclass of <instance>.

Class: <chained-method>

Class: <computed-method>

Class: <computed-emp>

These classes specify additional method objects with special properties. Each class is a subclass of <method>.

The following are the classes of Scheme numbers. Note that object-class will never return one of these classes; instead it returns an implementation-specific class that is associated with a particular numeric representation. The implementation-specific class is a subclass of one or more of these implementation-independent classes, so you should use these classes for specialization.

Class: <number>

Class: <complex>

Class: <real>

Class: <rational>

Class: <integer>

These are the classes of the Scheme numeric tower. <number> is a direct subclass of <math-object>, <complex> is a direct subclass of <number>, <real> is a direct subclass of <complex>, etc.

Class: <exact>

Class: <exact-complex>

Class: <exact-real>

Class: <exact-rational>

Class: <exact-integer>

These are the classes of exact numbers. <exact> is a direct subclass of <number>, <exact-complex> is a direct subclass of <exact> and <complex>, and in general, each is a direct subclass of preceding class and of the class without the exact- prefix.

Class: <inexact>

Class: <inexact-complex>

Class: <inexact-real>

Class: <inexact-rational>

Class: <inexact-integer>

These are the classes of inexact numbers. <inexact> is a direct subclass of <number>, <inexact-complex> is a direct subclass of <inexact> and <complex>, and in general, each is a direct subclass of preceding class and of the class without the inexact- prefix.